1. Technical Field
The present invention relates to a magnetic field measurement method using light and a magnetic field measurement apparatus.
2. Related Art
A magnetic field measurement apparatus using light can measure a weak magnetic field generated from a living body, such as a magnetic field (heart magnetic field) from the heart or a magnetic field (brain magnetic field) from the brain, and is expected to be applied to a medical image diagnostic apparatus or the like. In such a magnetic field measurement apparatus, pump light and probe light are applied to a gas cell in which gaseous alkali metals or the like are sealed. Atoms enclosed in the gas cell are excited by the pump light so as to be spin-polarized, and a polarization plane of the probe light which is transmitted through the gas cell is rotated according to a magnetic field due to the magneto-optical effect. A magnetic field is measured by measuring rotation angles of the polarization plane of the probe light before and after being transmitted through the gas cell (for example, JP-A-2013-108833).
In a general magnetic field measurement apparatus using an optical pumping method of the related art, a detection axis of a magnetic field is located in the same direction, and if directions of the detection axis and the magnetic field are different from each other, a projection component of the magnetic field onto the detection axis is measured. However, a magnetic field which is actually distributed in a space is expressed as three-dimensional vectors, and if a magnetic field is to be measured more accurately, magnetic fields in three-axis directions such as three orthogonal XYZ axes are preferably measured. Since a detection axis is located in a direction corresponding to an irradiation direction of probe light, it is necessary to cause the respective irradiation directions to be accurately perpendicular to each other in a case where the detection axes are increased by simply increasing the irradiation directions of the probe light. If an irradiation direction is tilted with respect to an expected direction, a detection axis is thus also tilted, and, as a result, errors occur in a measured value of a magnetic field which is expressed as three-dimensional vectors.